Combined cycle plant, control device thereof, and steam turbine startup method

Abstract

To provide a combined cycle plant, a control device thereof, and a steam turbine startup method that are aimed at improving the operability of a combined cycle plant by allowing a quick change of the output. A combined cycle plant is provided with: a gas turbine having a compressor, a combustor, and a turbine; a supplementary firing burner that raises the temperature of exhaust gas of the gas turbine; a heat recovery steam generator that generates steam using exhaust heat of the exhaust gas; a steam turbine that is driven by steam generated by the heat recovery steam generator; and a control device that changes both an output of the combustor and an output of the supplementary firing burner when an output of the combined cycle plant is to be changed.

1 . A combined cycle plant comprising:
 a gas turbine having a compressor, a combustor, and a turbine;   a supplementary firing burner that raises a temperature of exhaust gas of the gas turbine;   a heat recovery steam generator that generates steam using exhaust heat of the exhaust gas;   a steam turbine that is driven by steam generated by the heat recovery steam generator; and   a control device that changes both an output of the combustor and an output of the supplementary firing burner when an output of the combined cycle plant is to be changed.   
     
     
         2 . The combined cycle plant according to  claim 1 , wherein
 the control device has:
 a first output change mode in which the output of the combustor is changed and the output of the supplementary firing burner is held constant when the output of the combined cycle plant is to be changed; and 
 a second output change mode in which both the output of the combustor and the output of the supplementary firing burner are changed when the output of the combined cycle plant is to be changed, and 
   the control device is capable of selectively switching between the first output change mode and the second output change mode according to a switching signal.   
     
     
         3 . The combined cycle plant according to  claim 2 , wherein the control device selects the first output change mode at startup of the steam turbine, and switches to the second output change mode after completion of warming up of the steam turbine. 
     
     
         4 . The combined cycle plant according to  claim 2 , wherein the control device selects the first output change mode at startup of the steam turbine, and switches to the second output change mode before an output of the steam turbine reaches a maximum output that is achievable with steam generated using only exhaust heat of exhaust gas of the gas turbine. 
     
     
         5 . The combined cycle plant according to  claim 2 , wherein
 the control device has a third output change mode in which the output of the combustor is changed when the output of the combined cycle plant is to be changed, and after a preset predetermined output is reached, the output of the supplementary firing burner is changed, and   the control device is capable of selectively switching between the second output change mode and the third output change mode according to a switching signal.   
     
     
         6 . The combined cycle plant according to  claim 5 , wherein the control device has:
 a first operation mode in which both the output of the combustor and the output of the supplementary firing burner are changed when the output of the combined cycle plant is to be changed at startup of the steam turbine, and after a target output is reached, the output of the combustor is preferentially changed in response to a variation in the target output; and   a second operation mode in which the output of the combustor is held constant and the output of the supplementary firing burner is changed in response to a variation in the target output.   
     
     
         7 . A control device of a combined cycle plant, the combined cycle plant comprising:
 a gas turbine having a compressor, a combustor, and a turbine;   a supplementary firing burner that raises a temperature of exhaust gas of the gas turbine;   a heat recovery steam generator that generates steam using exhaust heat of the exhaust gas; and   a steam turbine that is driven by steam generated by the heat recovery steam generator,   the control device being configured to change both an output of the combustor and an output of the supplementary firing burner when an output of the combined cycle plant is to be changed.   
     
     
         8 . A method of starting up a steam turbine in a combined cycle plant, the combined cycle plant comprising:
 a gas turbine having a compressor, a combustor, and a turbine;   a supplementary firing burner that raises a temperature of exhaust gas of the gas turbine;   a heat recovery steam generator that generates steam using exhaust heat of the exhaust gas; and   a steam turbine that is driven by steam generated by the heat recovery steam generator,   the method comprising the steps of:
 increasing an output of the combustor at startup of the steam turbine; and 
 increasing both the output of the combustor and an output of the supplementary firing burner after completion of warming up of the steam turbine.